ATTITUDE SENSING ARRAY

Abstract: A sensing array (10) is disclosed, suitable for joystick, virtual reality and similar applications in controlling a display. The array is formed from tilt sensors (11), such as mercury switches, arranged to define different degrees of attitude in the sensed plane. Separate planes are defined for each sensed parameter.

Description: ATTITUDE SENSING ARRAY Technical Field The present invention relates to sensing mechanical states, and to a device for sensing, particularly for providing data to computer controlled systems, such as visual displays, virtual reality systems, and automatic and manually controlled systems. Background Art Various devices have been used to control the movement of objects on computer screens, both in the context of games and of application software. Examples include various forms of joystick, mouse and trackball devices. These all provide a simulated movement on the screen in response to a change in position of mechanical parts on the device, for example movement of the ball in a mouse or trackball. These devices are ergonomically unsound and have been linked with use-related injuries. They require a reference plane to be provided by, for example, a desk top. More recently, various devices have been proposed for use in so-called virtual reality systems. These devices tend to be expensive, and rely on complex sensor arrangements arranged in a glove or the like, hard wired to a relatively powerful processor. Such devices rely on a triangulation method to locate the hand held or operated part within a limited field. It will be appreciated that the complexity and difficulty of triangulation increases drastically with the possible sensing volume, and that accordingly severe practical limitations apply to accuracy and range with such systems. US patent No. 4445011 to Hansen discloses a joystick device connected by cable to a game machine. The joystick includes 4 tilt switches adapted to detect movement of the joystick forward, backward, left and right. US Patent 4425488 to Boyd discloses a system, for use by the handicapped, for indicating the direction of movement of a cursor by tilting left, right, and the like. Other documents, such as US Patent No. 4425488 to Moskin, and WO 91/15842 by Jacobs, disclose control arrangements using simple tilt switches in a joystick type arrangement. None of these systems has met with substantial commercial success, for various reasons. One problem is the lack of ability to sense distinctions between fine and gross movements of the sensing system. Thus, it is difficult with only single tilt sensors in any given direction to provide differently for small and large movements. Additionally, these devices all seek to simply provide an alternative implementation to conventional contact switch based joysticks. It is an object of the present invention to provide a sensing method and device which is relatively simple and inexpensive, yet provides comparable or superior performance to more complex devices. Summary of Invention According to one aspect the present invention provides a sensing array, comprising a plurality of sensing sub-arrays each adapted to sense orientation in a given plane, each sub-array comprising a plurality of sensors adapted to sense orientation about a given axis, each of said sensors adapted to sense at a particular angle to the normal, wherein in at least one sub-array sensors are provided which define at least two different angles on each side of the normal. According to a further aspect the present invention provides a method for sensing attitude utilising an array of sensing means, each sensing means adapted to sense attitude relative to gravity, said sensing means being arranged so as to define attitude within given planes, said method comprising periodically determining the state of each sensing means; processing the outputs of each of said sensing means; and producing a signal indicative of the attitude of said array within said planes. The present invention seeks to overcome the disadvantages of the prior art by recognising that the fundamental physical measurement required in many systems is attitude, not position. What is generally required in many systems , such as when controlling a display, or in many virtual reality systems, is not absolute position within a 3-D volume, but pitch and roll data. It is the type of movement being performed which is required to be sensed. This drastically reduces the amount of both information and processing required, while maintaining or increasing accuracy. Moreover, these are more intuitive variables than cartesian movement of a conventional joystick, or the absolute positioning of an object in a predefined volume. The present invention provides sensing outputs based on the orientation, or more correctly change in orientation, of the sensor relative to gravity - hence, no other reference plane is required for the device. Thus, the present invention enables control based on attitude, which is meant in the sense of the angle made by the axes of the device relative to the ground. In particular, what is sensed in not merely tilt left, right, forwards or backwards, but rather the extent and rate of such movement in the planes of measurement. This is described in the specification and claims as variable attitude. The sensor comprises an array of tilt sensors, preferably mercury switches, arranged so as to sense in different planes. The array is such that the measured variable is not merely, say, left or right, but how far the sensor is oriented left, and the array facilitates sensing also how quickly the shift was made. This allows for more complex information processing by the respective computer system, enabling a better description of the movement to be determined. A further advantage of the inventive arrangement is that there are no wearing parts within the sensing array. Conventional joystick type controls involve moving electrical and mechanical contacts, which inevitably wear over time. Brief Description of Drawings An illustrative embodiment of the present invention will now be described with reference to the accompanying figures, in which: Figure 1 illustrates the principle of the inventive attitude sensor; Figure 2 illustrates schematically the inventive control arrangement; Figure 3 shows schematically an illustrative transmitter arrangement for the remote device; Figure 4 shows schematically an illustrative receiver base station; Figure 5 illustrates a suitable mercury switch; Figure 6 illustrates orientation of the switch in use; Figure 7 illustrates one arrangement of the switches in use; Figure 8 is a boolean diagram of one embodiment of X-axis sensing; Figure 9 illustrates suitable angles in this embodiment; Figure 10 illustrates a perspective view of the parts of an X-axis encapsulation according to the present embodiment; Figure 11 is a boolean diagram of an alternative embodiment of the X- axis sensor; Figures 12 and 13 are views similar to figures 9 and 10 for the alternative implementation; Figure 14 is a boolean diagram of one implementation of the Y-axis sensor; Figure 15 shows suitable angles for the Y-axis sensors; Figure 16 shows an encapsulation for the Y-axis sensors; Figure 17 illustrates the operation of the Y-axis array; Figure 18 illustrates an assembly incorporating the X and Y axis sensor arrays; and Figure 19 illustrates in section one physical implementation of the present invention within a joystick type device. Detailed Description The following description refers to the general principles of the present invention according to a single embodiment. It is emphasised that whilst the mercury switch array shown and described is presently preferred, the invention is not limited to this device, and alternative sensor arrangements may be provided within the present invention. It is noted that other types of conductive fluid switches may be substituted for mercury switches, although mercury switches are presently preferred. This application is related to co-pending PCT application claiming common priority by the same applicant, entitled "Sensor Data Processing" and "Improvements to Attitude Sensing", the disclosures of which are incorporated herein by reference, and to which the reader should refer if further information is required in relation to applications for the array disclosed according to the present invention. The preferred arrangement uses a mercury switch array to sense roll and pitch of the sensing array. Throughout the specification, roll and pitch are referred to as x and y for the purposes of brevity, however it is emphasised that the parameter measured by the inventive array is attitude, in particular roll and pitch. Referring to Figure 1 , an array 10 of mercury tilt switches 11 forms the preferred basic attitude sensing device according to the present invention. The switches 11 occupy different alignments to allow for sensing of different degrees of tilt. Such switches are of conventional type, employing a glass capsule 14, a pair of contacts 12, and a small quantity of mercury 13. Tilting causes the switch to be open or closed depending upon the degree of tilt. Such switches have been experimentally determined to be very reliable in use, and very robust. An additional advantage is the inherent digital output - any given switch is either on or off, and so can be directly input to digital processors. By determining which switches are on or off, and preferably also considering which were previously on or off, a determination of attitude can be made. Preferably, the array is formed in a plastic or resin moulding 15, so that high precision is possible in the arrangement, even in a volume manufacturing situation. Ant suitable technique may be used to connect the portions of the array. It will be appreciated that while mercury switches are preferred, any suitable tilt sensor could be employed in the inventive arrangement. The attitude sensor is preferably contained within a hand held device, so as to function like a joystick in a conventional system. However, the system does not require a mechanical joint as in a joystick - the reference plane is provided by gravity. It will also be understood that the inventive system is applicable to related but distinct applications, such as mouse and trackball type system replacement, and to sensing attitude based on movements of other parts of the body. For example, the inventive arrangement may be used in a virtual reality type application to sense head movements, so as to control a display and show an appropriate field of view, or to sense movements of other parts of the body. Several devices according to the present invention may be employed simultaneously, using different or common base units. However, for the sake of clarity the joystick-type device will be used to illustrate the principles of the invention. Figure 5 shows the internal physical dimensions which have been found experimentally to perform satisfactorily. The switch is preferably about 11 mm long, with an internal width of 2.4 mm, and wall thickness of about 0.8 mm. The switch is preferably substantially circular in cross section. Contacts 12 are placed at one end of the switch. Of course, other types of conductive fluid switches may be substituted if desired. The type of mercury switch illustrated is widely available commercially. The switches may be of evacuated, non- evacuated or inert gas filled type - very little difference is observed in practise according to the present invention, as there is no arcing problem as currents and voltages are low. Referring to figure 6, two possible orientations of a mercury switch are shown - what will be discussed hereafter as normal and rotated orientation. In the normal orientation as shown, the switch contacts are aligned substantially horizontally with respect to gravity, whilst in the rotated orientation they are vertically displaced. To provide the best performance in practise, the switches in the array should be positioned in the normal orientation. Figure 7 illustrates the preferred x-axis, or more properly, the roll sensor arrangement. Three mercury switches 30, 31 , 32 are arranged at various orientations on one side of the normal, corresponding to roll in one direction, and three switches 33, 34, 35 similarly on the other side, with corresponding angles from the normal on the other side. This allows for the sensing of variable attitude, as progressively more switches open as attitude is increased. Figure 8, corresponding schematically to figure 7, illustrates that as more roll is introduced, successive sensors break contact, and this is the basis for the embodiment shown in figures 9 and 10. Figure 9 shows an illustrative set of angular placements for the switches in the roll sensor. It will be understood that these are exemplary only, and that other angles may be selected if desired. Preferably, a is about 12°, b is about 35°, and c is about 55°. Figure 10 shows a possible encapsulation arrangement for the roll sensing array.The array is encapsulated in an enclosure formed from halves 19, 19'. Each switch is placed in a respective cavity 20, which ensures that it is in the correct angular position. Additionally, it is preferred that the shape is such as to cause the switch to assume the normal orientation. A cable duct 21 allows for electrical connection to each switch. Locating devices 22,23 allow for accurate mating of the halves of the encapsulation. The two halves19, 19' mate so as to enclose the switches. Figures 11 to 13 show an alternative arrangement for the roll array in which instead of the contacts being normally closed and opening when tilted, the switches are normally open and close when tilted. Referring to the schematic diagram of figure 11 , switches 40 to 45 have closed contacts only as the array progressively changes in attitude.The arrangement is otherwise similar with variations, as will be apparent to those skilled in the art, to the geometry. The same angles of a, b and c are preferred as in the first arrangement Figures 14 to 17 show in more detail an arrangement for the Y-axis, or pitch , sensor. Experiment has established that only 2 switches are necessary for each sensor, rather than three as is preferred for the roll sensor. Referring to figure17, two switches 50,51 are arranged on one side of the normal in the plane, and two other 52, 53 on the other. Figure 14 shows schematically that the switches break contact once the attitude of the array passes the predefined angles. Referring to figure 15, it is preferred that a is about 150, and b is about 40° . It will be appreciated that it is possible to provide a Y-axis sensor arrangement wherein the normal state of the switches is open, by analogy to the X-axis alternative arrangement previously described with reference to figures 11 to 13. Figure 18 illustrates one way of constructing an assembled sensor array according to the present invention. All the individual sensors can be assembled into a unit suitable for incorporation into a hand held device. The units may be sized so as to stack neatly, as shown.The references to up, down etc correspond to the references on figures 16 and 10. To derive the maximum advantage from the inventive sensor array, it is desirable to employ software which receives and processes the switch outputs and interprets them as required, for example to drive a computer display. The full details of a preferred arrangement for utilising the sensor data derived from the inventive array are provided in the applications incorporated by reference as noted above, however, an outline is provided below. Referring to Figure 2, in block form the overall arrangement provides for the attitude sensor to provide output to a transmitter unit, which encodes the data for transmission to a base unit, which in turn may drive a conventional joystick port or the like. It will be appreciated that the embodiments described are intended to be illustrative and not limitative of the scope of the invention. The components will be described in more detail below. This arrangement provides a fully autonomous remote unit, which is relatively low cost, yet provides a high slew rate sensing mechanism. The design allows for a small number of active components. The device is microprocessor based , and does not require any initial complex alignment procedure to be carried out. The present invention may be employed if desired using a hard wired link, but a wireless link is preferred, and is far superior in practical operation. Referring to figure 3, switch data, which is quantised attitudinal data values in two axes (x, y for convenience - although strictly roll, pitch), is processed by the transmitter unit. Referring to Figure 3, x and y data is received asynchronously in parallel and encoded into 3 bit binary formats by two conventional encoder i.c.s. The encoders may be 8-bit priority encoders, for example, HEF 4532 devices from Signetics, or CD 4532 from RCA. The processing is preferably performed by an integrated circuit microcontroller, such as an XC68HC05K0 device from Motorola. The connections and operation of such devices are well known to those skilled in the art, and conventional techniques may be used for their implementation. Other devices may be substituted, as would be well understood. Data may also come from keypads (preferable for certain applications) and additional indicators, e.g. fire buttons. In the illustrative embodiment, the six encoded data lines are grouped with 2 fire data outputs to form an 8 bit data bus as input to the microprocessor. Raw data is oversampled and latched before presentation to firmware embedded in the processor, which performs five major functions: 1 ) dynamic modification of pitch data using pre-defined modelling 2) 'intelligent' redundancy analysis and 'bandwidth' expansion 3) features enhancement e.g. Autopilot, mode switching etc. 4) power management including AutoSleep (i.e. no OFF switch is required) 5) parallel to serial conversion with Pulse Position Modulation encoding The Y-axis data is processed to provide improved practical performance. Absolute sensor movement is modified by temporal modulation algorithms , so as to reduce the need for gross movements in the Y-axis by the user. This more closely approximates to normal intuitive responses. It further provides a predictable small state change response to Y-axis movements. The processing asymmetrically synthesises pseudo-states to dynamically expand the bandwidth of sensor data. This latter occurs asynchronously to X-axis data. The processing further allows for pre-emptive response to rapid state change demands. The IR transmission protocol selected is power efficient, and the encoding is provided by the microprocessor. Suitable transmitter components are commercially available. The IR transmission protocol is unlikely to provide interference with domestic appliances which are carrier based. The corresponding receiver has a wide capture angle, allowing for the minimisation of range and alignment problems in use. An IR signal is output from the transmitter via (in this embodiment) an LED, preferably a wide-angle transmission unit. This may be, for example, a SFH 485P device available from Siemens. Referring to Figure 4, the IR signal is detected by the IR phototransistor, pre-amplified, noise reduction applied (AGC, high pass filtering, pulse stretching etc.) to provide an interrupt line input for the microprocessor. Any conventional phototransistor may be used. The pre-amplifier may be an SL 486 device from Plessey Semiconductors. The microprocessor may be a XC68HC05K0 device from Motorola. The embedded receiver firmware performs four major functions: 1 ) serial to parallel conversion of Pulse Position Modulated data stream 2) error checking/data validation 3) dynamic modification of roll data using modelling techniques including x, y correlation 4) digital selection of appropriate resistor values to provide a 5 synthetic proportional output. X-axis data is decoded and processed, so as to improve the operation in practice. Absolute sensor movement is modified by temporal modulation algorithms, so as to linearise apparent acceleration, and provide predictable small state change response, and dynamic overshoot analysis and control.Pseudo- 10 states are synthesised asymmetrically to dynamically expand the bandwidth of sensor data. This synthesis occurs asynchronously to Y-axis data. Cross- correlation of X and Y axis data is performed , so as to permit illegal state changes to be suppressed. The output is derived from two standard analog switching i.c.'s driving an 15 optimised resistor array. This decoder/driver arrangement may utilise an 8- channel analog multiplexer, such as a CD 4051 from National Semiconductor, or alternatively a 3 bit decoder such as a 74HC138 from National Semiconductor, with appropriate transistor drivers. This array replicates the variable resistors normally found in proportional joysticks, but suffers from none 20 of the usual drift problems caused by wear and tear on the resistance elements. The hand piece is preferably designed to exploit the natural attitude sensing abilities of the bridge formed between the thumb and fingers when the hand is held as if you were about to 'shake hands.Such a design enforces a particular holding attitude, and this is further enhanced by displacement of the 25 centre of gravity. An example of a suitable handpiece is shown in section in figure 19. Handpiece 70 may be, for example, formed as a plastic moulding in two or more portions. Sensor arrays 71 , 72 are arranged close to the centre of gravity of the handpiece 70. the upper surface of the handpiece 70 includes autopilot button 30 74, a mode switch 73, and directional dial 75. the main PCB 76 includes most of the electronic hardware components, and drives output LED 79. Auxiliary controls 77, for example fire buttons, are positioned appropriately for users, and connected to secondary PCB 80. Power is derived from replaceable batteries, for example AAA type dry cells. it will be appreciated that the present invention is applicable to many applications and implementations other than those described herein. The attitude sensor and sensing system are applicable to other virtual reality type applications other than that described.

Claims: CLAIMS 1. A sensing array, comprising a plurality of sensing sub-arrays each adapted to sense orientation in a given plane, each sub-array comprising a plurality of sensors adapted to sense orientation about a given axis, each of said sensors adapted to sense at a particular angle to the normal, wherein in at least one sub-array sensors are provided which define at least two different angles on each side of the normal. 2. An array according to claim 1 , wherein sub-arrays are provided which are adapted to sense roll and pitch. 3. An array according claim 2, wherein the sub-arrays adapted to sense roll and pitch each comprise sensors which define at least two different angles on each side of the normal within their respective planes. 4. An array according claim 3, wherein the sub-array adapted to sense roll includes sensors which define at least three different angles on each side of the normal. 5. An array according to any one of the preceding claims, wherein the sensors comprise conductive fluid switches. 6. An array according to claim 5, wherein said sensors are mercury switches. 7. A controller device operatively adapted to control a computer device, including an array according to any one of the preceding claims. 8. A controller device according to claim 7, wherein said controller device is adapted to directly or indirectly control a display device. 9. A sensor system for a virtual reality system, including one or more arrays according to any one of claims 1 to 6. 10. A method for sensing attitude utilising an array of sensing means, each sensing means adapted to sense attitude relative to gravity, said sensing means being arranged so as to define attitude within given planes, said method comprising periodically determining the state of each sensing means; processing the outputs of each of said sensing means; and producing a signal indicative of the attitude of said sensing means within said planes.

Inventors: WALKER PETER JOSEPH MICHAEL, WALKER, PETER, JOSEPH, MICHAEL
Applicants: BALLAR PTY LTD, WALKER PETER JOSEPH MICHAEL, BALLAR PTY. LTD., WALKER, PETER, JOSEPH, MICHAEL
Application year: 1994
Main classification: G06F3
IPC codes: G01C9, G06F3